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Climate skeptic claims prebunked by Keeling

Posted on 21 August 2012 by Ari Jokimäki

If you have followed discussions about global warming, you probably have seen claims that because atmospheric carbon dioxide concentration is measured on the top of a volcano (actually on the side - the measurement station is at the elevation of 3400m while the top of the mountain is at the elevation of over 4100m), and that volcanos emit carbon dioxide, the carbon dioxide measurements cannot be trusted.  Thus the argument concludes that we don't know if atmospheric carbon dioxide concentration is rising or not. Here we take a look at what Charles David Keeling (1928 - 2005) wrote long ago.

Charles David Keeling in the lab

As many of you probably know, Keeling was the one who arranged atmospheric carbon dioxide measurements starting in the 1950s, that resulted in the famous Keeling Curve, which describes the evolution of atmospheric carbon dioxide as measured in Hawaii, on top of a volcano called Mauna Loa. The measurement site was selected, because Hawaii is located in the middle of an ocean and far away from disturbing carbon dioxide sources. Also, the elevation of the location of the station ensures that measured air masses are representative of large areas. However, as the Keeling Curve is famous and is drawn from the measurements that originate at a site that has volcanic vents nearby, it is quite natural that there are claims made that the presence of the volcano somehow invalidates all our knowledge of atmospheric carbon dioxide. Many readers of course know that it isn't so, but here we look at what Keeling wrote about the issue in 1960. It turns out he had already debunked the claims, even before those claims were made.

In 1960, Keeling published the paper The Concentration and Isotopic Abundances of Carbon Dioxide in the Atmosphere (full text freely available in the linked abstract page). In this paper he discussed results from carbon dioxide measurements during a few years of observtions. Early in the paper he says:

"Three gas analysers, as described by SMITH (1953), equipped with strip chart recorders, have been employed to measure the concentration of carbon dioxide continuously at stations in Antarctica, Hawaii, and California."

So already from the beginning of Keeling's measurements there were other measurement stations besides Mauna Loa. End of story? Well, pretty much so for those claims, but anyway, let's take a look at what other things Keeling has to say on the subject.

Despite the reality, what if Mauna Loa was the only atmospheric carbon dioxide measuring station as those claims suggest? Would carbon dioxide measurements be suspect because of that? Keeling discusses this too. Keeling notes that there was local contamination in all of the measurement stations. In the Antarctica station there was some combustion of fuel near the station:

"It could be readily spotted from the significant fluctuations in the otherwise steady trace of the recorder pen and was eliminated from consideration in the initial reading of the charts."

In Mauna Loa, there also was some extra variability in the measurement record:

"This is attributed to release of carbon dioxide by nearby volcanic vents; combustion on the island associated with agricultural, industrial, and domestic activities; and lower concentration of carbon dioxide in the air transported to the station by upslope winds."

It seems that Keeling was well aware that "Mauna Loa is a volcano". He also identified some other sources of contamination. Not only was Keeling aware of the situation, he also knew how to correct it:

"The values reported here are averages of data for periods of downslope winds or strong lateral winds when the concentration remained nearly constant for several hours or more."

At a California measurement station there was an interesting situation. The measured carbon dioxide concentration was found to be highly variable:

"Highest concentrations occur during light winds from the north, from the direction of Los Angeles; lowest concentrations when the wind is from the west or southwest and of moderate force or greater."

Highest concentrations when winds were blowing from a large city? Why is that? Could it be that there is carbon dioxide coming from human actions?

Keeling then proceeds to discuss seasonal variation which he finds in the Northern Hemisphere but not in the Southern Hemisphere. Based on carbon-13 measurements, he concludes that the seasonal variation found in the Northern Hemisphere is from the activity of land plants. He also notes that timing of maximum and minimum concentrations match the timing of the land vegetation activity in the Northern Hemisphere. Keeling explains the absence of seasonal variability in the Southern Hemisphere by the smaller area of vegetation in the Southern Hemisphere.

Getting back to the claims of CO2 record contamination, Keeling then discusses the interannual trends in carbon dioxide concentration:

"Where data extend beyond one year, averages for the second year are higher than for the first year. At the South Pole, where the longest record exists, the concentration has increased at the rate of about 1.3 p.p.m. per year."

Note that Keeling reported the first clear increase in carbon dioxide concentration from the South Pole, not from Mauna Loa.

So, already back in 1960, Keeling knew that Mauna Loa was a volcano. He also knew how to correct the problems that the volcano caused for carbon dioxide measurements. He also knew that the volcanic problems wouldn't matter anyway because there were other measurement stations that were nowhere near any volcanos, and those stations show the same thing as Mauna Loa station - atmospheric carbon dioxide concentration is rising.

See also "Mauna Loa is a volcano" (also available as intermediate and advanced versions).

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Comments 1 to 10:

  1. I tend to think that the measurments from Cape Grim might go someway to debunk this meme as well!
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  2. I have an email from Piers Tan from the Mauna Loa observatory debunking a claim regarding this issue made by Plimer in his book. I'll dig it up after work, Eli Rabett picked up on it and has a post about it on his blog somewhere.
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  3. Brilliant. When I learned about d13C measurements, and TA carbon fluxes and looked at the CO2 pumhandle here I thought people knew about this stuff since ~1980, as pumphandle starts from there. It turns out Charlie knew that since 1960... Big time hats off to him. And big time scorn at denialists who keep agnoring such exceptional piece of science.
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  4. Here we go, one of my prouder moments ;) It's amazing where forum discussions can go!
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  5. It strikes me that given that Mauna Loa provides a 50+ year instrumental record of CO2 concentration that it provides pretty much the gold standard for CO2 measurement in the late 20th century/early 21st century scientific record. Personally - I don't see how anyone could retain credibility and also claim that CO2 has not risen within the 20th century - at the very least.
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  6. I don't know what to say. It's incredible there is (still) a need to debunk well established stuff like this. Sad.
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  7. What I find amusing is that given that the measurements are next to a volcano and allegedly volcanoes chuck out huge amounts of CO2 sporadically. The keeling curve is surprisingly smooth. I guess the volcano is intelligent and lets out just enough CO2, even when it has a bit of a build up. OK lets assume it doesn't belch a load of CO2 sporadically, the graph shows that there would be a constant amount interfering with readings all the time. So deduct whatever that mythical amount is and you still get a graph with a positive slope! Are some skeptics saying that the atmospheric CO2 produces a flat line and CO2 from the volcano has risen uniformly for 50 odd years, producing a curve?? That would be easily proven, so lets see the proof.
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  8. Steve Ryan published a paper on the effect of the volcano on the MLO record. Suffice it to say, slim to none Most impressive are how aircraft measurements match the MLO record over a period of more than a year, showing that MLO does indeed measure CO2 in the free troposphere.
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  9. Oh yes, you can see the variability in the MLO record at one of the links above, with a link to where you can download the hourly data, so no Paul, that dog don't hunt neither
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  10. You can actually read global CO2 levels in a busy city as well since on windy days the CO2 concentration would move towards the global mean. I saw a very nice graph somewhere showing this by plotting wind speed and read CO2 levels where you could clearly see the measurements approaching the global mean.

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